Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous translumenal angioplasty (PTA) and percutaneous translumenal coronary angioplasty (PTCA). These therapeutic techniques are well known in the art and may typically involve the use of a balloon catheter and a guide wire, possibly in combination with other intravascular devices. The balloon catheter is advanced over the guide wire such that the distal end of the balloon catheter is positioned adjacent a restriction in a diseased vessel. The balloon is inflated and the restriction in the vessel is thus opened.
Balloon catheters are commonly categorized into three main types according to their guide wire compatibility; over-the-wire (OTW), fixed-wire (FW), and single-operator-exchange (SOE). OTW, FW, and SOE as used hereinafter refers to the conventional design of such catheters. Examples of OTW, FW and SOE catheters may be found in U.S. Pat. Nos. 5,047,045 to Arney et al., 4,943,278 to Euteneuer et al., and 5,156,594 to Keith et al., respectively. The entire disclosure of the above listed patents is hereby incorporated by reference.
OTW catheters are used in combination with a guide wire which is removably insertable therein. The guide wire extends through a full length guide wire lumen inside the OTW catheter. As such, distal pressure measurements, distal fluid injections, and guide wire exchanges may be facilitated through the guide wire lumen. OTW catheter exchanges may be facilitated by the use of an extension wire or a guide wire captivation device.
SOE catheters are also used in combination with a guide wire, but the guide wire extends through a distal guide wire lumen which is inside only a distal portion of the catheter and the remainder of the guide wire remains exposed outside the catheter. As such, a SOE catheter may be readily exchanged over a conventional length guide wire. However, SOE catheters do not readily provide a conventional means to exchange a guide wire without the use of ancillary equipment. Furthermore, SOE catheters do not provide a conventional means for distal pressure measurement and/or distal fluid injection.
By contrast, FW catheters are typically used without a guide wire and as such have a relatively small profile. FW catheters incorporate a built-in core wire which serves some of the same functions as a guide wire. The core wire, however, is not removable and thus the FW catheter is not exchangeable over the core wire. In addition, FW catheters do not provide a conventional means for distal pressure measurement and distal fluid injection.
Although FW catheters generally provide an advantage in profile and although SOE catheters generally provide an advantage in rapid catheter exchange, OTW catheters are considered the more versatile of the group and as such are favored for the majority of clinical applications.
In terms of catheter shaft construction, the proximal shaft portion of an OTW catheter must be designed to contain the guide wire and also provide a path for inflation fluid to inflate the distally located balloon. Thus, the proximal shaft portion of an OTW balloon catheter includes a guide wire lumen and an inflation lumen. By contrast, both SOE catheters and FW catheters only include an inflation lumen in the proximal portion of the shaft. SOE catheters do not require a guide wire lumen in the proximal portion of the shaft because the guide wire is external to the proximal catheter shaft. FW catheters do not require a guide wire lumen in the proximal portion of the shaft because FW catheters are not constructed to be used with removable guide wires. Since the proximal shaft portion of an OTW catheter must accommodate a guide wire lumen and since FW and SOE catheters do not need to accommodate a guide wire lumen, the profile (outside diameter) of the proximal shaft of an OTW catheter is inherently larger than the profile of either a FW or SOE catheter.
In addition to the inherent profile requirements discussed above, the optimal design of a proximal shaft section of an OTW balloon catheter must account for other performance criteria. For example, it is desirable to have a proximal shaft section which is the smallest possible profile, highly pushable (i.e. longitudinally stiff) yet easily coiled for temporary storage and resistant to damage resulting from in-vitro handling (i.e., latitudinally flexible). High performance FW and SOE catheters typically utilize a metallic proximal shaft section (commonly referred to as a hypotube) with an outside diameter on the order of 0.032 inches and a wall thickness on the order of 0.003 inches. Practicing physicians have found the profile, pushability, ease of handling and other performance aspects of these hypotube-type FW and SOE catheters superior by comparison to non-hypotube-type FW and SOE catheters. Similarly, OTW catheters which utilize a hypotube for a proximal shaft section provide enhanced pushability with low profile. However, since the profile of an OTW catheter is inherently larger than a FW or SOE catheter, the latitudinal stiffness of an OTW catheter utilizing a hypotube proximal shaft is undesirably high. As such, the hypotube shaft on an OTW catheter tends to be more difficult to manage in-vitro and more prone to damage during handling.
In view of the advantages of a metallic proximal shaft section and in view of the advantages of an OTW catheter design discussed earlier, it is desirable to have an OTW catheter with a metallic proximal shaft section which is easy to manipulate in-vivo, easy to manage and resistant to damage from in-vitro handling.